The low basal oxygen consumption rate of the ATP5B-KO3.1 cells, similar to that of ρ0D5 cells, was not unexpected as these cells lack ATP synthase activity, leaving the proton motive force exclusively for importing nuclear-encoded mitochondrial proteins, calcium influx etc. Of note, tumour cells with OXPHOS levels as low as 3% of parental 4T1 cells (ρ0D5) could generate lung metastases (ρ0D5LM) and were not auxotrophic for uridine and pyruvate. The gene discussed is ATP5F1B; the disease is neoplasm.